1. Field of the Invention
The present invention relates to oxygen concentrators.
2. Description of the Related Art
Recently oxygen concentrators and liquid oxygen are normally used as oxygen supplying methods in the field of home oxygen therapy.
There are many patients with respiratory failure who take treatment with supplemental oxygen at home in the field of home oxygen therapy. Such patients take oxygen that is concentrated to approximately 90%, from home oxygen supply sources which generally include oxygen concentrators and liquid oxygen.
For the oxygen concentrators, ones with the function which adsorbs nitrogen in the air have been developed. This method includes PSA (pressure swing adsorption) in which selective adsorbent for nitrogen is put in the cylinder and oxygen and nitrogen in the air are separated by repetition of pressurization and depressurization, PVSA (pressure vacuum swing adsorption) in which minimum pressure is lower than atmospheric pressure and maximum pressure is larger than atmospheric pressure, and VSA (vacuum swing adsorption) in which maximum pressure is equal to or lower than atmospheric pressure and minimum pressure is lower than atmospheric pressure.
In this type of oxygen concentrators, PSA or PVSA circuit comprises a plurality of oxygen concentration columns (usually two) comprised of oxygen concentrating catalysts such as zeolite, and supplies alternately concentrated oxygen to patients via oxygen tank.
In this regard, PSA or PVSA circuit is connected to the oxygen tank through the flow channel for concentrated oxygen airtight. To supply concentrated oxygen gas at a stable oxygen concentration, the pressure from the said circuit to the oxygen tank (hereinafter referred to as pressure within the system) always needs to be set within a predetermined range depending on the capacity and concentration of oxygen concentrating catalysts and other conditions such as temperature in the oxygen concentration columns.
Previously, pressure control in such system has been conducted by placing control valves in between oxygen concentration columns and the oxygen tank, always monitoring the pressures in oxygen concentration columns and the oxygen tank, and then controlling the valves depending on the monitored pressure (International Publication WO2005/035037 Pamphlet (full text)).
However, many components and means for controlling these components have been required to control pressure in the system in the prior art.
Therefore, the structure becomes complex, and it makes the oxygen concentrator expensive and power consuming. It also makes maintenance of the concentrator difficult.
Accordingly, the task of the present invention is to provide oxygen concentrators which achieve reliable pressure control in the oxygen columns with reduced number of components for pressure control in the oxygen columns and also easy maintenance and reduced power consumption.
Another task of the present invention is to provide oxygen concentrators with high oxygen concentration efficiency.